1. Field of the Invention
The present invention relates to a method of forming a gate recess of a semiconductor device, a method of manufacturing an AlGaN/GaN-HEMT (High-Electron Mobility Transistor), and an AlGaN/GaN-HEMT.
2. Description of the Background Art
A conventional structure and a method of manufacturing an AlGaN/GaN-HEMT, having a recessed-gate structure and normally-off characteristics (enhancement mode), are disclosed in Ken Nakata, et al., “Normally-off AlGaN/GaN HEMT with Recessed Gate for High Power Applications” Technical Report of the Institute of Electronics, Information and Communication Engineers (IEICE), pp. 51-56, ED2005-129, CPM2002-116, LQE005-56, Oct. 2005.
According to the solution, by dry etching such as inductively-coupled plasma reactive ion etching (ICP-RIE), an opening is formed in a SiN surface protective film at a position where a gate electrode is formed later, a gate recess is formed in a UID (Unintentionally Doped)-AlGaN electron supply layer, sometimes referred to as “UID-AlGaN layer”, to a depth approximately 5 nm above a two-dimensional electron gas (2DEG) layer, by which the threshold voltage Vth is controlled, and a gate electrode is formed in the opening, to thereby manufacture a normally-off AlGaN/GaN-HEMT.
However, since the gate recess of the normally-off AlGaN/GaN-HEMT of the prior art is formed by dry etching, so that the gate recess may tend to vary in the depth, or may be damaged due to plasma ion, and thereby the threshold voltage (Vth), which is a critical electrical characteristic of the normally-off AlGaN/GaN-HEMT, may undesirably vary.